The long-range objective of this research is to advance our understanding of the process of protein secretion, especially in endocrine glands. Attention will be focused on the Golgi complex, and the participation of its components in secretion. The work will be carried out largely on anterior pituitary cells, but other cells which may represent favorable objects for the study of specific aspects of the secretory process will also be used in these investigations. Specific aspects of the secretory process which have been selected for study in depth are: 1) the mechanism of concentration and packaging of secretion granules; 2) the route of flow of secretory proteins within the various elements of the Golgi complex; 3) the distribution of Golgi functions among its various elements; 4) the procedures used by the cell to recover and redistribute membrane following exocytosis of secretion granules; and 5) the mechanisms involved in separating the flow of secretory protein and lysosomal enzymes. The approach used to investigate these problems will involve a combination of techniques including electron microscopy, cell fractionation, autoradiography, enzyme cytochemistry, immunocytochemistry, column chromatography and polyacrylamide gel electrophoresis.